There are many instances in which enhanced braking capabilities for material handling equipment are desirable. Such capabilities are particularly desirable for crawler-type drive tractors with right-hand and left-hand crawler drive tracks. Because such crawler-type drive tractors are used for a variety of material handling functions, effective braking and precise control for maneuverability are required for efficient operation in areas having restricted space and/or irregular hilly terrain.
Transmission systems for crawler-type drive tractors known previously have been developed which include a clutch and a steering brake for each of the crawler dual tracks. These clutches and steering brakes are selectively hydraulically actuated through mechanical linkages which control hydraulic cylinders and valves.
In many crawler track transmission systems currently in use, hydraulic actuation of the brake for one of the crawler tracks results in disengagement of the clutch for that track, thereby disconnecting the track from the engine of the implement. Clutch disengagement is usually effected hydraulically by providing hydraulic fluid lines which are operatively associated with the brake cylinder for one of the crawler tracks and its respective clutch. Disengagement of the clutch for the track being braked, while the clutch of the other crawler track remains engaged, permits the operator of the implement to execute a so-called pivot turn for manuevering the implement.
While many crawler track transmission systems operate as described above, it will be appreciated that in some instances, disengagement of the crawler track clutches attendant to application of the track brakes is not desirable. This is particularly true when the crawler implement is being used on hilly or irregular terrain. When used on such terrain, it is frequently desirable to take advantage of the braking effect provided by the implement's internal combustion engine to slow the implement. Of course, this requires that the clutches connecting the crawler tracks with the engine remain engaged. However, as noted, many systems function to disengage the track clutches when the track brakes are applied, thus precluding application of the brakes if the clutches connecting the implement engine to the crawler tracks are to remain engaged. Consequently, most previous systems have not been capable of providing both engine braking and normal track braking simultaneously.
In view of the shortcoming of previously known transmission systems, it is desirable to provide a control system which provides enhanced implement braking by permitting application of the crawler track brakes without disengagement of the track clutches so that engine braking is simultaneously provided. Selectable use of such braking capabilities is also desirable, bearing in mind that the system must not impair the normal manueverability of the implement. Preferably, such a system should be readily fabricated and installed, and should be straightforward in construction to facilitate reliable operation.